The field of application of the invention is digital projection, in particular for digital cinema. The projection objective finds application, for example, as a base objective with an anamorphic attachment.
Projectors used in digital cinema are distinguished through a beam-splitting prism between the chips and the objective. The glass path is up to 119.5 mm, which causes a longitudinal chromatic aberration, as well as a spherical aberration. These aberrations must be corrected by the projector objective. Thus, objectives calculated for other circumstances are fundamentally unsuitable.
Mainly, zoom objectives are offered on the market. However, for fixed installations, a zoom objective is not necessary. Moreover, the conversion of the chip format to the image format 2.35:1 advantageously takes place in digital cinema with the aid of an anamorphic attachment. In order to reduce the dimensions of the attachment and thus the costs, it is necessary that the screen side pupil not be too far away from the front lens. This goal is difficult to achieve with zoom objectives.
Described in DE 103 53 563 B4 is an objective with fixed focal length that meets the requirements. However, in all of the specified embodiment forms, this objective contains an aspherical surface, which increases the production costs.